A typical prior art frequency multiplexed broadband transmission system is described in "Electronics Letters" 22nd Oct. 1987, Vol. 23, No. 22, pages 1196 to 1198.
In all examples described there, the carrier frequencies used are in a single, continuous frequency band which i snot more than one octave wide and lies in a frequency range which is the higher the more signals have to be transmitted. If, for example, only four signals have to be transmitted, the carriers will lie in a frequency band extending from 150 to 300 MHz, and if 60 signals have to be transmitted, the 60 carriers will lie in a frequency band from 2.7 to 5.2 GHz. This frequency allocation corresponds to a frequency allocation which is known from "IEEE Transactions and Communications", Vol. COM-29, No. 6, June 1981, pages 868 to 885, especially FIG. 13 on page 878. The modulation there is amplitude modulation, and the carrier frequencies lie within a single octave in a frequency band from 54 to 108 MHz.
The conventional manner of choosing carrier frequencies is disadvantageous in that if a great number of signals have to be transmitted, only frequency bands in the high frequency range range, e.g., the GHz range, can be used, so that frequencies in lower ranges, in which signal processing can also be performed by simpler means, will not be used.